Microwave heating



May 26, 1953 T. P. KINN: 2,640,142

MICROWAVE HEATING Filed 061;. 4 1946 WITNESSES: INVENTOR ATTORNEY Patented May 26, 1953 JSTATJES OFFICE "MICRQWAVE HEATING Theodore .P. sKinn, I'Baltimore, MIL, :assignor to -;Wmtinghuse Electric, Corporation, East rPittsburgh, .Pa :a corporation 0f Pennsylvania Application October-=4, 1946,'Serial"No. 701,308

My invention relates to the heating 01' elongated "electricity insulating' filamentary material by -means of a high frequency energy fin the micro-wave region.

-It is a an object of my invention to treat elon gated filamentary =mateiials such as thread or narrow ribbons made of cotton, plastics, zrube her, paper, or any other material or substance generally recognized asbeing 1 insulating with respect to the conventional forms :of electrical power commercially universally available at the present time. The treatment may be (for "the purposes of drying, curingysettingor any other purposes; 'and I accomplish this-by":means ofan extremely simple and economical structure. through which the elongated -material may he passed continuously.

It is-a further object of "my l'l'lVfilfltlOIl-tOllJlW- vide electrical apparatus for the purpose described which is energizable with alternatingcurrent frequencieshaving wave lengths in the order of several centimeters, say .10, sand :less, although somewhat higher Wave lengths are utilizable. "Preferably-the I heatingportion ofcth'e apparatus :consistsonly-of a hollow outer conductor which is at ground potential and the electrical energy is-yconfined inside of the outer conductor. .Theconductor may be in the form of a resonant chamber or Wave guide. Preferably, (the-filamentary material is passed through theconductor parallelzto thez electric field therein. This means, of course, that the conductor .is preferably'operated with a modeio'f 1 energy transmission prov-idingan intense electric field along substantially: the full length of the portion oi? the material passing through it.

:Features, objects, innovations and :methods provided by my mventionwilltbediscernible from the followingdescription which isto be taken in conjunction with the accompanying drawing, in which:

Figure 1 is a schematic View showingsrectangular cavity resonator jfor cheating thread of insulating material.

Fig. 2 is a schematic View of a similar apparatus for heating a thread or other filamentary material in steps, and

Fig. 3 is a modified form of apparatus for similarly heating a plurality of elongated insulating filaments by a single return bend wave guide.

Textiles such as rayon and nylon must be cured, dried and twisted. Rubber thread material, both synthetic and pure latex, must be cured. Such operations usually require heating .2 and high production requires that such operations be carried out while "the materiali-stravelling at liighrspeed. The apparatus herein described makes it possible "tocouple energy into the material 'at a rate suitable 'for high production requirements.

Referring' to' ffi'i'g; 1, a. rectangular copper oavity resonatoror envelope z'can be energized in any suitable mannenand Ischematically'show aimeansiforitransferring energyto it as comprising .ta' wave guide t .coupled to the cavity TBS- onator 22 by means-of :a perforated diaphragm t. The ends 8 and :lt cif the cavity resonator are provided with holes It! at their'centers through whichsan elongated filamentary material it is threaded and-continuously moves. Pulleys it at the rentrance, rend ot-the :cavity resonator and pulleysifiat the exit e-nd lreep the material i /I inrsuitable'i tension sothatdt does not flap around inside the cavity. "Theplilleys 'lil may be metallic and .groundedrto remove any charge that the material might :pick up. Ifhe apparatus herein described :is especially 1 suitable for heating =circular threads. Accordingly, the :holes W. are shown :as :circular, but :they can be otherwise formed tor-harmonize with the cross section of the material being heat-treated. 'Ihe. apparatus shown in :1 heat *treats the. thread M only a single-:ti-me "but .fOl longer ?heat treatments, or for :shorter apparatus, an. :arrangement such shownsin. Fig. .iz-may be used.

Referring 2170 Fig.2, a resonant cavity 253 has a :plurality' of spaced (openings .12 2 f in a -side 12:4 oi the cavity resonator land a similarrgroup oi open" ings in the opposite side thereof, with each opening in one 'of :.the.-sides longitudinally aligned with an opening in the other @Slllfi. Thread :26 is threaded through "longitudinally aligned: opcningsrinzthe: manner shown with per time coming TOIltHQf" the cavityresonator and boingmeturmbent bymeans 0f pulleys 28 onone side :of rthecavityzresonatorrandpulleys 38 on the: l0lTlI613Sld8'.. Thesapulleys may, :ifld-esired, bezmadezof "metal and grounded. As 517118 1 thread enters and re-enters the cavity resonator a plurality of times, it is repeatedly heated in increments. Obviously, the portions of the thread outside the resonator can be short. If other intermediate treatments are desired, they can be longer and, if desired, more widely spaced.

Rather than using a cavity resonator, I also contemplate the use of a wave guide, as illustrated schematically in Fig. 3. In this embodiment, a plurality of separate threads 3| are passed rectilinearly through a tortuous wave guide 32 having a plurality of return bends 34 interconnecting straight portions or sections 36. Opposite sides of the straight portions 35 are provided with a plurality of aligned spaced holes 35 through which the threads or other filamentary material is passed. As each portion of the material passes through a section 36 of the wave guide 32, it is heated so that, in the embodiment shown in Fig. 3, each filament is subjected to heating five times. However, it is obvious that the number of return bends is a matter of design or choice.

In all embodiments, the holes are preferably midway along the associated sides and the filamentary material passes through the cavity resonator or the wave guide, as the case may be, substantially parallel to the electric field vector.

While I have described my invention in connection with threads, it is obvious that fine ribbons can similarly be treated, in which case the holes in the conductors comprising the cavity resonators or wave guides can be shaped correspondingly. In the case of the cavity resonator, it is sometimes desirable to make the displacement between the entrance and exit of a thread portion about one-half a Wave length, as disclosed and claimed in my concurrently filed application, Serial No. 701,305. However, my invention is not thus limited.

In all of the embodiments the actual structure in which the elongated filaments are heated consists only of an outer metallic shell of metal which does not require any metal parts inside of it.

While I have used the word filamentary or filaments for describing the elongated material to be heat treated, it is obvious that I use this term only in the lack of a more generic term for such material, but I do not desire to be limited, and the invention is obviously not limited to extremely fine threads which are hardly visible. It is also obvious that my invention is subject to wide application for other materials and is capable of being applied in many other ways.

I claim as my invention:

1. A high-frequency heating apparatus comprising a micro-wave conductor comprising a single metallic envelope comprising a return-bent wave guide having a plurality of sections extending in the same general direction between bends, each section having a pair of opposite sides, each of which is provided with a plurality of longitudinally spaced holes, and means for passing material through said sections in a plurality of paths each of which includes a hole in each of said opposite sides of a plurality of said sections, so that the material passes successively through said sections.

2. A high-frequency heating apparatus comprising a micro-wave conductor comprising a single metallic envelope comprising a return-bent wave guide having a plurality of sections extending in the same general direction between bends, each section having a air of opposite sides, each of which is provided with a plurality of longitudinally spaced holes with pairs of holes in each section in registry, so that elongated material may be passed through each pair of registered holes, means for guiding material longitudinally through said pairs of registered holes so that the material passes successively through said sections, and means for energizing said wave guide so as to provide an electric field substantially parallel to a plane including the lines between said pairs of registered holes.

3. High frequency heating apparatus for heating a dielectric filament, comprising a microwave energy-transfer hollow conductor having an inside space adapted to be electrically stressed by microwave energy therein, said conductor having a pair of sides each of which is provided with a plurality of holes, means for delivering microwave energy to said conductor for establishing an electric field therein, and guiding means for guiding a dielectric filament for continuous and successive passage through said conductor via said holes, in a, direction substantially parallel to the direction of the electric field inside said c0n ductor, said guiding means comprising a metallic member which is electrically grounded and in contact with said filament, said metallic member being external to said conductor at the materialexit side thereof.

4. A high frequency heating apparatus including a resonant microwave energy-transfer conductor having at least a first side and a second side, said first side being opposite in position relative to said second side, each of said sides being provided with an equal plurality of openings, each of said openings in said first side corresponding in position to one of said openings in the second side, such that a single elongated workpiece can be successively passed through said conductor between respectively corresponding openings in said first and second sides, with means for energizing said conductor so as to provide an electric field therein, and the direction of movement of said workpiece through said conductor being parallel to said electric field,

Skilling, Physical Behavior of Wave Guides, Electronics, March 1943, pages 76430.

Electronic Heat, Steel, November 12, page 92, 

